Medical device operating with x-rays and method for operating same

ABSTRACT

The invention relates to a medical device operating with X-rays, comprising: an X-ray source, from which an X-ray beam that has an intensity maximum along a central ray can be emitted, a rotation unit, with which the X-ray source can be rotated about an isocenter, wherein the central axis of the X-ray beam is oriented eccentrically to the isocenter such that, in particular upon rotation about the isocenter, the central rays emitted from different spatial directions are tangential to an imaginary circle around the isocenter. Furthermore, the invention relates to a method for operating a medical device, comprising the following steps: providing an X-ray source, from which an X-ray beam that has an intensity maximum along a central ray is emitted, rotating the X-ray source about an isocenter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of InternationalApplication No. PCT/EP2011/051459 filed Feb. 2, 2011, which designatesthe United States of America, and claims priority to DE PatentApplication No. 10 2010 009 019.0 filed Feb. 24, 2010. The contents ofwhich are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to a medical device operating with x-rays, inparticular a radiation therapy device, as well as method for operatingthe same.

BACKGROUND

The irradiation of a finite target volume by means of x-rays fromdifferent spatial directions, such as is implemented for instance forthe purposes of imaging in diagnostic methods or dose synthesis intherapeutic methods, usually requires as homogenous a gross illuminationof the target volume as possible.

Since the x-ray sources usually have a preferred beam direction, alongwhich the maximum dose is located, and the beam direction is usuallyaligned toward the center of the target volume, the illumination of theboundary areas of the target volume is usually reduced compared with thecenter of the target volume.

The problem with radiation therapy devices and with imaging devices waspreviously solved by a beam flattening filter, which flattens thecentral portions of the radiation lobe and thus homogenizes the profileof the x-ray beam.

SUMMARY

In one embodiment, a medical device operating with x-rays may comprise:an x-ray radiation source, with which an x-ray radiation cone can beemitted, which has a maximum intensity along a central beam, and arotation apparatus, with which the x-ray radiation source can be rotatedabout an isocenter, wherein the central axis of the x-ray radiation coneis aligned paraxially past the isocenter.

In a further embodiment, the central axis of the x-ray radiation cone isaligned paraxially past the isocenter such that upon rotation around theisocenter, the central beams emitted from different spatial directionsare tangential to an imaginary circle around the isocenter. In a furtherembodiment, the device is embodied as a radiation therapy device. In afurther embodiment, a collimator exists in the radiation path of thex-ray radiation cone for lateral delimitation of the beam profile of thex-ray beam. In a further embodiment, no beam flattening filter which isused for spatial dose homogenization is arranged in the radiation pathof the x-ray radiation cone.

In another embodiment, a method for operating a medical device maycomprise: providing an x-ray radiation source, with which an x-rayradiation cone is emitted, which has a maximum intensity along a centralbeam, and rotating the x-ray radiation source about an isocenter,wherein the central axis of the x-ray radiation cone is directedparaxially past the isocenter.

In a further embodiment, the central axis of the x-ray radiation cone isdirected paraxially past the isocenter such that upon rotation aroundthe isocenter, the central beams emitted from different spatialdirections are tangential to an imaginary circle around the isocenter.In a further embodiment, no beam flattening filter used for spatial dosehomogenization is arranged in the radiation path of the x-ray radiationcone. In a further embodiment, the x-ray radiation cone is collimated.

Another embodiment provides a use of an x-ray radiation cone, which hasa maximum intensity along a central beam, which, with a medical deviceoperating with x-rays, is emitted by an x-ray source from differentspatial directions about an isocenter, for dose homogenization in anarea around the isocenter, by the central beam of the x-ray radiationcone being aligned laterally past the isocenter in each spatialdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be explained in more detail below withreference to figures, in which:

FIG. 1 shows the principle of dose generation in a radiation therapydevice according to the prior art, and

FIG. 2 shows the principle of dose generation in a radiation therapydevice according to an example embodiment of the present invention.

DETAILED DESCRIPTION

Some embodiments provide a medical device operating with x-rays, whichenables a rapid and efficient illumination of a target volume.Furthermore, some embodiments provide a method with which it is possibleto illuminate a target volume rapidly and efficiently.

Some embodiments provide a medical device operating with x-rays, whichmay include:

-   -   an x-ray radiation source, with which an x-ray can be emitted,        which has a maximum dose along a central beam, and    -   a rotation apparatus, with which the x-ray radiation source can        be rotated about an isocenter,    -   wherein the central axis of the x-ray beam is aligned        eccentrically to the isocenter, so that in particular upon        rotation around the isocenter, the central beams emitted from        different spatial directions are tangential to an imaginary        circle around the isocenter.

Certain embodiments are based on the knowledge that the radiation lobeof an x-ray source, in other words the x-ray cone emitted by the x-raysource, usually has a maximum along the central beam. The radiation lobeof the x-ray source is now no longer directed at the center, but insteadmore at the boundary area. The irradiation therefore takes placeparaxially and/or tangentially from different spatial directions.

By rotating the source around the target volume, a significantly morehomogenous illumination of the entire volume is achieved on the whole,even if the radiation lobe itself indicates an inhomogeneous doseprofile. The more homogenous illumination is enabled by the combinationof inhomogeneous dose profile of the radiation lobe, which flattensaround a maximum dose along the central beam, an eccentric alignment ofthe radiation lobe and of the rotation of the radiation lobe.

The geometric arrangement and alignment of the x-ray source togetherwith the rotation of the x-ray source therefore contribute to thehomogenization of the illumination.

Compared with previous solutions, in which the homogenization is largelyeffected by an absorber, a significantly improved efficiency of thex-ray source can be achieved.

The absorber can namely be embodied such that it absorbs less radiationpower, since it no longer has to cater for the homogenization of thedose profile on its own. It can even be completely omitted, so that thecomplete dose output of the source strikes the target volume. The lattercase is free of beam flattening filters used for homogenization in thex-ray radiation path. Overall, it is therefore possible to dispense witha lossy, radiation-blasted absorber.

The dose rate with which a target volume can be illuminated increases asa result. The irradiation duration depends on the fraction (desireddose)/(local dose rate) formed across the tumor volume. The site to beirradiated at which the minimal dose rate occurs, in other words theleast irradiated region, therefore defines the irradiation duration.Time can therefore be reduced using the medical device disclosed herein.

With an inhomogeneous dose distribution, it also applies that locationsirradiated at the same time with higher dose rates are protected fromthe radiation for a part of the irradiation duration, since otherwise anexcessively high dose would be applied there. A more homogenous dosedistribution also solves this problem. Locations with an excessivelyhigh dose rate need not be masked out after a short period of time, e.g.with a collimator, so that the desired dose can be applied with a lowerdose rate at another location.

In particular, the device can be embodied as a radiation therapy device,for instance with a therapeutic x-ray radiation source, which can berotated about an isocenter.

A collimator can be present in the radiation path of the x-ray, withwhich the beam profile of the x-ray can then be laterally delimited andcan thus be adjusted to a target volume to be irradiated for instance.Only certain partial volumes can therefore be irradiated with an objectto be irradiated.

Some embodiments provide a method for operating a medical device,comprising:

-   -   providing an x-ray radiation source, with which an x-ray beam is        emitted, which has a maximum intensity along a central beam, and    -   rotating the x-ray radiation source about an isocenter, wherein        during rotation the central axis of the x-ray beam is aligned        eccentrically to the isocenter such that in particular upon        rotation about the isocenter, the central beams emitted from        different directions are tangential to an imaginary circle        around the isocenter.

In some embodiments, no beam flattening filter is arranged in theradiation path of the x-ray. The radiation path of the x-ray beam can becollimated in order to form the lateral profile.

In some embodiments, the x-ray beam, which has a maximum intensity inthe central beam and which, with a medical device operating with x-raysis emitted from an x-ray source from different spatial directions aboutan isocenter, is used to homogenize the dose in an area around theisocenter, by the central beam of the x-ray beam being aligned laterallypast the isocenter in each spatial direction.

With the aid of FIG. 1, the principle of dose generation about anisocenter in a radiation therapy device is explained according to theprior art.

The radiation therapy device 11 includes a rotatable gantry 13, withwhich an x-ray radiation source 15 can be rotated around the object tobe irradiated. A conical x-ray beam is directed at the isocenter 19 fromthe x-ray radiation source. The x-ray beam is laterally delimited by acollimator 17. The irradiation usually takes place from differentdirections by rotating the x-ray source 15 around the isocenter 19,indicated by the positions of the gantry shown with dashed lines.

The central beam 21 of the conical x-ray beam strikes the isocenter 19in the process. The x-ray beam in this way has a dose distribution 23,indicated by the Gaussian-type curve, which has a maximum dose along thecentral beam 21, which tapers toward the edge. If a target volume isirradiated with the particle beam, the dose rate in the isocenter 19 istherefore at its highest and attenuates toward the edge.

This principle is made clearly apparent by the applied dose generated bythe two irradiation directions shown opposite one another. The dosemaxima illuminate the target volume at the same point, so that the doseapplied by the two irradiation directions in the target volume has thesame inhomogeneous distribution as the inhomogeneous dose distribution23 in the x-ray beam.

A beam flattening filter (not shown here) is therefore generally used ina radiation therapy device 11 according to the prior art, said beamflattening filter being arranged in the radiation path of the x-ray beamand rendering the inhomogeneous dose profile more homogenous. Thishowever takes place at the cost of the radiation dose which is destroyedin the beam flattening filter.

FIG. 2 shows the principle of dose generation in an example radiationtherapy device 11 according to one embodiment of the present invention.

The central beam 21 of the x-ray source 15 is now no longer alignedtoward the isocenter 19, but aims paraxially past the isocenter. Uponrotation of the x-ray source 15 about the isocenter 19, this results inthe central beams 21 emitted being tangential to a circle 25 around theisocenter.

The dose which is set up around the isocenter 19 in geometricconfigurations of this type, is clearly more homogenous compared with adose which was applied when aligning the central beam 23 to theisocenter 19.

This is clearly apparent with the aid of the two irradiation directionsshown opposite one another. The maximum dose which is applied by therespective irradiation directions is now no longer in the isocenter 19,but instead respectively at an opposite point of the isocenter 19. Doseportions which clearly lie below the maximum dose are added together inthe isocenter 10 itself by the opposite irradiation. By adding the doseportions, a dose is applied in the isocenter 19, which is significantlycloser to the maximum dose than the individual dose portions themselves.A significantly more homogenous dose can be applied overall as a result.

Ideally it is therefore even possible to completely dispense with a beamflattening filter. No dose output is then destroyed in the beamflattening filter, as a result of which the target volume can beilluminated with a higher dose rate, which significantly reducesirradiation time.

Provision can also be made here for a collimator 17, which adjusts andrestricts the applied dose to a target volume.

Even if the principle was explained with the aid of a radiation therapydevice 11, the same principle of achieving a dose homogenization of thedose distribution set up about an isocenter 13 can be transferred toimaging devices operating with x-rays, such as for instance a computedtomography system (CT) or a cone beam CT.

LIST OF REFERENCE CHARACTERS

-   11 Radiation therapy device-   13 Gantry-   15 x-ray radiation source-   17 Collimator-   19 Isocenter-   21 Central beam-   23 Dose distribution-   25 Circle

What is claimed is:
 1. A medical device operating with x-rays,comprising: a rotation apparatus, a single x-ray radiation sourcemounted on the rotation apparatus, the single x-ray radiation sourceconfigured to emit an x-ray radiation cone having an inhomogeneousintensity profile which has a maximum intensity along a central beam anda lower intensity away from the central beam, wherein the rotationapparatus is configured to rotate the single x-ray radiation sourceabout an isocenter, wherein the single x-ray radiation source is mountedon the rotation apparatus at a fixed, non-isocentric angle relative tothe rotation apparatus throughout the rotation of the x-ray radiationsource about the isocenter, such that the x-ray radiation cone emittedby the single x-ray radiation source maintains a fixed angle relative tothe rotation apparatus throughout the rotation of the x-ray radiationsource about the isocenter, wherein the central axis of the x-rayradiation cone is aligned paraxially past the isocenter such that forany particular rotational position of the single x-ray radiation source,the intensity of x-ray radiation at the isocenter is less than themaximum intensity along the central beam of the x-ray radiation cone,wherein the fixed angle of the single x-ray radiation source relative tothe rotation apparatus is selected such that upon rotation of the singlex-ray radiation source, the central beam of the x-ray radiation conefollows a path that is tangential to an imaginary circle around theisocenter to provide a collective illumination near the isocenter thatis more homogenous than the inhomogeneous intensity profile of the x-rayradiation cone.
 2. The medical device of claim 1, wherein the device isembodied as a radiation therapy device.
 3. The medical device of claim1, wherein a collimator exists in the radiation path of the x-rayradiation cone for lateral delimitation of the beam profile of the x-raybeam.
 4. The medical device of claim 1, wherein no beam flatteningfilter which is used for spatial dose homogenization is arranged in theradiation path of the x-ray radiation cone.
 5. A method for operating amedical device, comprising: providing a single x-ray radiation sourcemounted to a rotation apparatus, the single x-ray radiation sourceconfigured to emit an x-ray radiation cone having an inhomogeneousintensity profile which has a maximum intensity along a central beam anda lower intensity away from the central beam, and rotating the singlex-ray radiation source about an isocenter, wherein the single x-rayradiation source is mounted on the rotation apparatus at a fixed,non-isocentric angle relative to the rotation apparatus throughout therotation of the x-ray radiation source about the isocenter, such thatthe x-ray radiation cone emitted by the single x-ray radiation sourcemaintains a fixed angle relative to the rotation apparatus throughoutthe rotation of the x-ray radiation source about the isocenter, andwherein the central axis of the x-ray radiation cone is directedparaxially past the isocenter such that for any particular rotationalposition of the single x-ray radiation source, the intensity of x-rayradiation at the isocenter is less than the maximum intensity along thecentral beam of the x-ray radiation cone, and wherein the fixed angle ofthe single x-ray radiation source relative to the rotation apparatus isselected such that as the single x-ray radiation source rotates aroundthe isocenter, the central beam of the x-ray radiation cone follows apath that is tangential to an imaginary circle around the isocenter toprovide a collective illumination near the isocenter that is morehomogenous than the inhomogeneous intensity profile of the x-rayradiation cone.
 6. The method of claim 5, wherein no beam flatteningfilter used for spatial dose homogenization is arranged in the radiationpath of the x-ray radiation cone.
 7. The method of claim 5, wherein thex-ray radiation cone is collimated.